1 将系统时间转换成UNIX时间戳
DateTime dtStart = TimeZone.CurrentTimeZone.ToLocalTime(new DateTime(1970,1,1));
DateTime dtNow = DateTime.Parse(DateTime.Now.ToString());
TimeSpan toNow = dtNow.Subtract(dtStart);
string timeStamp = toNow.Ticks.ToString();
timeStamp = timeStamp.Substring(0,timeStamp.Length - 7);
2将UNIX时间戳转换成系统时间
string timeStamp = "1144821796";
DateTime dtStart = TimeZone.CurrentTimeZone.ToLocalTime(new DateTime(1970,1,1));
long lTime = long.Parse(timeStamp + "0000000");
TimeSpan toNow = new TimeSpan(lTime);
DateTime dtResult = dtStart.Add(toNow);

//DateTimeUNIX，直接转换，不改变时区
DateTime dtStart = new DateTime(1970, 1, 1, 0, 0, 0);
TimeSpan toNow = dt.Subtract(dtStart);
int timeStamp = (int)(toNow.Ticks/10000000);